Apparatus for preconditioning chips in a digester



Aug. 25, 1959 S. A. SALMONSON APPARATUS FOR PRECONDITIONING CHIPS IN ADIGESTER Filed vDec. 20, 1954 2 Sheets-Sheet 1 v l o. 3% A g 109$ AD 5%AD QQM PRiOR ART //\/z/-/\ TUE SVEN A. SALMQNSON ,4 TTUFF/VE V5 S. A.SALMONSON Aug. 25, 1959 APPARATUS FOR PRECONDITIONING CHIPS IN ADIGESTER 2 Sheets-Sheet 2 Filed Dec. 20, 1954 //\/Z/E/\/ TE/FF 'SVENA.SALMON5ON United States Patent APPARATUS FOR PRECDNDTTIONING CHIPS [NA DIGESTER Sven A. Salmonson, Portland, Oreg. Application December 20,1954, Serial No. 476,480

3 Claims. (Cl. 162-246) This invention relates to an improved apparatusfor preconditioning chips in a digester, and the present application isa continuation-in-part of my co-pending application, Serial No. 291,626,filed June 4, 1952, for Method of and Apparatus for Packing Chips in aDigester, now abandoned.

In the art of pulp making, utilizing a chemical reduction of wood chipsin a digester, it is desirable that the chips be evenly distributed inthe digester, or, in other words, that the density of the mass of chipsin the digester be uniform throughout the digester. Uniform distributiondensity makes it possible for the cooking liquor to circulate evenlywithin the digester to cause the liquor penetration of the chips to beuniform, resulting in a high quality pulp. It has been endeavored toobtain such uniform mass density by the use of auxiliary equipmentcomprising steam injection means which pre-steams and distributes thechips as they are fed to the digester. Previous pre-steam means have notbeen entirely successful because the auxiliary equipment used thereforimpedes and retards the flow of chips into the digester and also retardsthe outward flow of air within the digester, it being desirable tofacilitate the escape of air from the digester when the digester isbeing charged, not only for the purpose of completing the chargingoperation more quickly, but also to exclude air from the chips as theypack in the digester for avoiding dilution of the steam atmosphere andfor permitting free circulation and uniform penetration of the cookingliquor. Portable apparatus heretofore proposed for pre-steamingtreatment is further objectionable because of the delay and manual laborinvolved in manipulating the apparatus in each charging phase of thedigester cycle, both of which factors increase operating costs.

It is, therefore, an important object of the present invention toprovide an improved chip digester having steam injection means whichpre-steams wood chips and distributes them in a uniform mass density inthe digester, and, more importantly, which permits free discharge oftrapped air in the digester to avoid the formation of air pockets in thechip mass; to provide a chip distributor having improved steam injectionmeans which permits the free flow of chips into said digester wherebythe loading of the digester can be accomplished with facility; and toprovide an improved chip distributor having automatic control meanswhereby steam injection nozzles therein are operative only when chipsare being fed to said digester.

The invention, in brief, resides in a novel chip distributor utilizingsteam injection means for pre-steaming wood chips as they are loadedinto the digester. The nozzles are mounted in the walls of the digesterand are directed radially inwardly for projecting steam into engagementwith chips being loaded into the digester. In an alternative embodimentof the invention, steam control means, actuated by moving wood chips, isprovided for automatically projecting steam only during the time thatthe digester is being charged. Air outlet or discharge means areprovided to prevent air from becoming trapped in the digester as it isbeing charged.

While the present apparatus is especially designed for the reduction ofwood chips in the production of paper pulp by the sulphite process, itis to be understood that fibrous material of other character may belikewise treated in the preparation of pulp for this and other purposesas the manufacture of nitrocellulose, cellulose acetate, pyroxylin,rayon and other analogous materials; likewise, the invention is notlimited to the sulphite method of reduction but may be applied to soda,sulphate, semi-chemical, and modified ground wood pulp treatment.

The invention will be better understood] and additional objects andadvantages will become apparent from the following description taken inconnection with the accompanying drawings which illustrate preferredforms of the invention. It is to be understood, however, that theinvention may take still other forms, and that all such modificationsand variations within the scope of the appended claims which will occurto persons skilled in the art are included in the invention.

In the drawings:

Figure 1 is a fragmentary sectional view through the top portion of thepresent digester, showing the air discharge means and one form of steamnozzle mounting arrangement;

Figure 2 is a sectional view taken on the line 2-2 of Figure 1;

Figure 3 is an elevational view of a prior art digester with a portionof said digester broken away;

Figure 4 is a fragmentary sectional view through the top portion of adigester showing an alternative form of nozzle mounting, and alsoshowing automatic steam control means for the nozzles; and

Figure 5 is a diagrammatic view of the steam control means.

Referring to Figures 1 and 2, 10 designates a chemical pulp digesteradapted to be charged with Wood chips 11 and adapted to subject thechips to a cooking liquor at elevated temperature and pressure forreducing the chips to pulp. Digester '10 has a charging inlet or filleropening passageway 12 in communication with a hopper v13, or other feedmeans, for feeding chips to the digester.

The digester is provided with a plurality of bores 18 adjacent the topfor receiving nozzles 20. Bores 18 open through bosses 21 on the outersurface of the digester 10, and apertured plates 22 are secured on thebosses by means of screws 23. The outer ends of nozzles. 20 are eachprovided with a check valve 25 and a control or throttle valve 26, andare connected to a manifold pipe 27 by T connections 28. Pipe 27 andnozzles 20 receive steam under pressure from a lead-in pipe 29 havingshut-off valve 30 therein.

As best seen in Figure 2, the bores 18 extend radially so that thenozzles 20 are directed toward the axis of the digester. The tips of thenozzles, however, are located back from the axis so that chips whichfall into the digester are in the path of steam being projected from thenozzles. With this nozzle mounting arrangement the inlet to the digesteris entirely open and free to receive the stream of chips and permit theescape of air from the digester whereby the digester can be rapidlycharged to reduce the batch time, and, in general, to increase the yieldof the digester.

With the arrangement above described, the chips fall freely into thedigester and are uniformly pre-steamed by jets of steam. The chips aredistributed evenly as the digester fills, and, with the absence of airpockets in the mass, the cooking liquor is permitted uniformly tocirculate in the mass, with the result that the temperature and liquorconcentration throughout the digester are uniform, resulting in a highquality pulp. The absence of air pockets furthermore permits tighterpacking of the chips and the digester is adapted to contain a largerchip charge. Figure 3 shows one type of prior art digester 10a whereinthe chips 11a fall by gravity in a conical pile. In this type ofstructure, air pockets will form in the mass of chips to cause a poorquality pulp to be produced. There is no steam pre-treatment.

Figures 4 and show a modified form of the invention. A digester 35having a charging inlet or filler opening 36 is adapted to be chargedwith wood chips 37 received from a hopper or other feed means 38.Digester 35 is provided with inclined bores 40 adjacent the top forreceiving nozzles 41. Bores 40 open through bosses 42 on the outersurface of the digester, and apertured plates 43 are secured on thebosses by screws 44. Nozzles 41 are each provided with a check valve 45and a control or throttle valve 46 at their outer ends and are connectedto a manifold pipe 48 by T connections 49. Steam is supplied to themanifold pipe 48 and the nozzles 41 through a lead-in pipe 50 having ashut-off valve 51 therein.

Bores 40 are in inclined positions so that the nozzles 41 are directedtoward the axis of the digester and are adapted to project steam onchips being fed through the filler opening 36. The steam projected fromthe nozzles pre-steams the chips and the angular position of the nozzlesforcefully drives the chips downwardly into the digester so that saidchips are firmly packed therein without air pockets formed in the chipmass.

This embodiment employs automatic steam control means actuated by thestream of chips falling through the filler opening, the automaticcontrol means being illustrated diagrammatically in Figure 5. Thecontrol means comprises a switch housing 55 having a lever arm 56pivotally mounted through an opening 57 in one end thereof and extendinginto the path of moving chips being discharged by the hopper or otherfeed means 38. The switch housing 55 could be mounted at any place inthe filler opening 36, but, preferably, as shown, it is carried in aspacer block 58 between the hopper and the top of the digester filleropening.

Switch lever arm 56 has an enlarged chip engaging plate 60 on its outerend and is pivotally mounted in a boss 61 formed as a part of a flexiblediaphragm 62 which prevents chips and dust from entering the switchhousing 55. The inner end of arm 56 is urged downwardly by a compressionspring 64 and engages a switch arm 65 which is biased upwardly by spring66. Switch arm 65, which comprises one contact of a switch, iselectrically connected to a lead wire 67 by means of a connector 68mounted in the Wall of the switch housing, and the arm 65 is adapted toengage a contact 69 connected to a wire 70 by means of a connector 71.The contacts are closed when the outer end of switch lever arm 56 ispivoted downwardly due to the falling chips in engagement therewith butin the rest position of the parts, arm 56 is pivoted upwardly to breakcontacts 65 and 69 as shown in Figure 5.

The closing of switch contacts 65 and 69 energizes a solenoid 75electrically connected to the wire 70 and a lead Wire 7012:. Solenoid 75has a plunger 76 connected to a lever 77 which operates a bypass valve78 enclosed in a housing 79. Valve housing 79 is connected to a fluidpressure line 80 and is provided with a relief port 81. Spring 82normally holds the valve closed against pressure line 80, as shown, whensolenoid 75 is de-energized.

Pressure line 80 has a shut-off valve 85 on the outlet side of valvehousing 79 and terminates in a valve housing 86 connected into the steamlead-in pipe 50. Housing 86 has a cylinder 87 at its upper end, a pairof chambers 89 at its lower end and a central bore 90 extending betweenthe cylinder 87 and one of the chambers 89. A valve stem 91 is .slidablein bore 90 and has a piston 92 on its upper end for movement in cylinder87, and a valve 93 on its lower end. Chambers 89 communicate by means ofan aperture 95, and aperture 95 is engaged by valve 93 to provide a seattherefor for controlling the flow of steam between the two chambers 89.Valve 93 is biased upwardly into engagement with its seat by spring 96carried on the valve stem between piston 92 and the bottom of cylinder87.

The operation of the control system is as follows. When no chips arepassing through the filler opening 36 of the digester, spring 64 holdsthe inner end of the arm 56 in a lowered position whereby switchcont-acts 65 and 69 are open. Fluid pressure is constantly maintained inthe pipe 80, and when the valve 78 is held by spring 82 in the positionshown in Figure 5, no fluid pressure is admitted to cylinder 87 of valvehousing 86 whereby the piston 92 and stem 90 are biased upwardly and thevalve 93 seats in the aperture 95. When the lever arm 56 is pivoted bymeans of a chip load thereon, the contacts 65 and 69 are closed andsolenoid 75 is energized to rotate the valve 78 to a position wherebythe inlet opening from pipe 80 into the housing 79 is opened and therelief port 81 is closed. Fluid pressure is thereby admitted to thecylinder 87 in valve housing 86 and the piston 92 is forced downwardlyto unseat the valve 93. Steam will thus flow through pipe 50 and willcontinue to flow until solenoid 75 is de-energized by reason of thecontacts 65 and 69 being opened when the arm 56 is permitted to moveupwardly to its rest position. In the de-energized position of thesolenoid 75, relief port 81 is opened, whereby fluid pressure which ispresent in the cylinder 87 can be relieved. Spring 96 then re-closes thevalve 93.

This embodiment also has air discharge means for facilitating the freeescape of air which may become trapped in the digester while thedigester is being charged. A vertical discharge pipe 100 is mounted inthe top wall of the digester and has a nozzle 101 and shut-ofi valve102. A portion of pipe 100 projects interiorly of the digester, and thisprojecting portion has a plurality of small vent holes 103 of a size topermit air to enter the pipe 100 but to prevent chips from passingtherethrough. The bottom end of the pipe may have vent holes orperforations therein similar to the lower portions of the side walls toassist in permitting air to escape through the discharge pipe. Thus withthe air escaping freely through pipe 100 there is no back pressure inthe digester to retard the entrance of chips in a substantially solidstream through the inlet opening 36 and the charging time is reduced toa minimum. The rate of steam injection is controlled so thatsubstantially all the steam is condensed on the old chips and no steampressure is produced to retard the free fall of the chips through inletopening 36. After charging, the vent valve 102 is closed.

The present arrangement of nozzles is designed to deliver steam at anunusually fast rate in order to enhance the effectiveness of thepre-steaming treatment. The best results have been otbained with a steamflow at the rate of twenty thousand to twenty-five thousand pounds perhour at a steam pressure of to pounds per square inch. With thischaracter and intensity of treatment, the chips are well distributed andpre-steamed, causing the digester to be uniformly packed and causingsubstantially all the air to be excluded and driven out through the ventpipe. In the use of prior portable devices for this purpose insertablethrough the charging opening, it is found that a steam flow at as high arate as only eight thousand pounds per hour in a digester of the samesize causes objectionable air lock which interferes with the freeflowing of the chips into the digester. Such a low rate of steamintroduction has been found insuflicient properly to pre-steam the chipsand accomplish the improved results of the present invention.

Having now described my invention and in what manner the same may beused, what I claim as new and desire to protect by Letters Patent is:

1. A digester for the chemical reduction of fibrous material, such aswood chips, to pulp comprising, a digester wall having a top portionwith a vertical central charging inlet passageway which is adapted to beclosed during a cooking operation, a plurality of steam nozzles mountedin and projecting through a portion of said wall around said passagewayof greater diameter than said passageway and directed approximatelyhorizontally and radially inwardly immediately below said top wallportion and the lower end of said passageway, said nozzles being spacedfrom the center of the projected area of said passageway and projectingonly slightly into said projected area to discharge jets of steamradially into the center of a falling stream of said material introducedthrough said passageway, said inlet passageway being unencumbered andunobstructed for the substantially unimpeded rapid admission of saidmaterial.

2. A digester as defined in claim 1 including an air vent pipe for thedigester projecting through said top wall portion, and a valve in saidpipe.

3. A digester as defined in claim 1 including steam supply meansconnected to said nozzles, valve means in said steam supply means, acontrol element having an actuating member projecting into the path ofsaid stream of material, and means operated by actuation of said controlelement to open said valve when said actuating member is deflected bysaid material.

References Cited in the file of this patent UNITED STATES PATENTS1,813,205 Scholz et a1. July 7, 1931 1,998,875 Koda Apr. 23, 19352,029,086 Svensson Jan. 28, 1936 2,451,073 Cowherd Oct. 12, 19482,475,850 Moore et a1 July 12, 1949 2,483,426 Moore Oct. 4, 19492,614,923 Tarkkonen Oct. 21, 1952 FOREIGN PATENTS 537,749 Germany Nov.6, 1931 59,371 Norway May 16, 1938

